The invention relates to minimizing RF channel interence.
The number of products incorporating the recently approved Bluetooth wireless standard is expected to explode during the first couple years of the new millennium. Bluetooth, which establishes wireless connections between devices such as mobile phones, PDAs, and headsets, operates at relatively low data rates over short distances using very little power. On the other hand, IEEE 802.11 is a wireless LAN standard approved by IEEE a couple years ago and operates at higher data rates over longer distances using more power. Companies today are strongly benefiting from using 802.11-compliant wireless LANs to support efficient mobile communications between handheld data collectors and corporate IS databases.
Because of a high demand for both wireless PANs and LANs, it's important that Bluetooth and 802.11 coexist in close proximity. A current problem, though, is that the two standards operate in the same 2.4 GHz unlicensed radio band and equally use frequency hopping modulation. This commonality poses a strong potential for radio frequency interference.
Interference happens when Bluetooth and 802.11 devices transmit at the same time near each other. This causes a destruction of data bits, prompting the system to retransmit entire data packets. A wireless LAN node (like Bluetooth or 802.11) that works on a principle of carrier sensing will not transmit when it senses other stations transmitting. If placed in close proximity to 802.11-based wireless LANs, Bluetooth could cause interference. Modern LANs keep working despite such interference, but performance can suffer. Much design effort in Bluetooth—including limits on physical range and use of spread-spectrum frequency hopping—went toward avoiding conflict with other transmission schemes.
The likelihood is that Bluetooth products will likely jam the operation of 802.11, not the other way around. The reason is that Bluetooth hops through frequencies 600 times faster than 802.11. While an 802.11 device is transmitting on a particular frequency, a nearby Bluetooth product will most likely interfere with the 802.11 transmission many times before the 802.11 device hops to the next frequency. This barrage of radio signals emanating from Bluetooth products could seriously degrade the operation of an 802.11 network.
Additionally, other wireless products such as GPS can also cause interference. Bluetooth works in the 2.4-GHz range of the radio band, which is not licensed by the FCC and is inhabited by cell phones, baby monitors and the IEEE 802.11 LAN. With multiple independently operated radio frequency systems, potential problems arise, including self-jamming, inter-modulation products, increased shielding requirements, tight filtering requirements, among others. For example, the Bluetooth band is around 2.4 Ghz. One of the cellular bands is around 900 Mhz. In many Bluetooth transmitters, the waveform is modulated at 1.2 GHz and multiplied by two to get to 2.4 GHz band. Additionally, a number of wireless transceivers use local oscillators that are at around 1 to 1.1 GHz to give an intermediate frequency (IF) of about 100–200 MHz The RF frequency is thus about 1.2 GHz. Hence, when Bluetooth and wireless transceivers operate simultaneously, potential RF interference problems exist.